Attrition-mill



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(No Model.)

T. L. STURTEVANT 8v M; G. DAVIS.

. ATTRITION MILL. No. 372.436. x. Patented Nov. 1, 1887-.

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(No Model.) 2 Sheets-Sheet 2.

T. L. STURTBVANT L M. GQDAVIS. 'ATTRLTION MILL.

No. 372.436'. Patented Nov. 1, 1887.

UNITED STATES PATENT OFFICE.

THOMAS rL. STURTEVANT, OF FRAMINGHAM, AND MILTON G. DAVIS, OF

` SOMERVILLE, MASSACHUSETTS.

ATTRlTlON-MILL.

SPECIFICATION forming pait of Letters Patent No. 372,436, dated November 1, 1887.

Application tiled July` 30, 1856. Serial No. 209,510. (No model.)

To all whom, it may concern.:

Be it known that we, THOMAS L. S'IURTE- vANT and MILTON G. DAvIs, citizens of the United States, residing at Framingham and Somerville, in the county of Middlesex and State of Massachusetts, have invented certain new and useful Improvements in Attrition- Mills; and we do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same, reference being had to the accompanying drawings, and to letters or figures of reference marked thereon, which form a part of this specification.

This invention relates to attrition mills or screens, more particularly that class in which the screening-surface is composed of a series ofsimilar sections or screen-plates, which form the screen as an entirety, and which are removable for repairs, or replacement when worn out.

Our improvements relate to the peculiar construction and arrangement of certain of the sectional screenplates, which form a roof or approximately A-shaped screen, as shown in Figure 2 of the drawings, projecting into the interior ot' the mill, whereby a largely-increased screening-snrfaceis obtained, the novel features of which will be hereinafter more fully described and claimed.

Our invention is especially adapted to suit a certain class of attrition-mills, in which two oppositely-rotating heads cooperate with the case of the mill in the reduction or grinding of hard material or mineral-bearing rocks. In mills of this class the interior of the milleasing is eircularin form and usually provided with a screen-holder, partly circular in form, which retains the screening portion formed by plates affixed upon its interior.

In operating these attritionmills, so rapid is the reduction ofthe material that every possible means must be adopted in order t0 expedite the removal of the comminuted material and pass it rapidly away to prevent clogging of the mill, and thereby secure its greatest efficacy.

The drawings represent in Fig. l a vertical transverse section of an attrition-mill containing our screen. Fig. 2 is a longitudinal vertical section of the same on line x x, Fig. 1. Fig. 3 represents a perspective view of one of our screen-plates. Fig. 4 is a partly-sectional elevation, enlarged, of aseries of screen-plates of the form shown in Fig. 3 in position. Fig.

5 is a perspective view, and Fig. 6 a cross-secis passed. Below the screen is formed a passage, C, which connects with said screen, whereby all the ground material capable of passing through the latter is delivered and conveyed to proper storagereceptacles. Laterally of the said casing A are disposedtwo rotary heads, D D, actuated by suitable shafts and provided with two circular hollow bushings, E E, which project slightly into the millcasing. Vhen the mill is in operation, one head revolves rapidly in one direction and the other runs with equal velocity in the reverse direction, or both may run in the same direction.

The interior of the mill is provided with a series'of screen-plates, a a a, arranged in circular form and supported upon rings b b, which are V-shaped in cross section and secured to the casing A. rIhis screening-surlce is eonstrncted of a series of plates which Inay be Varied in form. Thus in Fig. 2 the platesaa are perforated with conical holes c c, with the apex of the cones directed toward the interior of the mill; but in Figs. l, 5, and 6 a different form of plate, a a', is shown, which may be substituted with equally good results. These latter screen-plates are truncated prisms in crosssection, and are curved exteriorly at d, Fig. 6, to conform to the contour of rings b b, by which they are supported. In lieu of being perforated the plates a are provided with lateral wedge-shaped ribs c e, disposed on either side of said plates, and provided alternately with recesses f f and lugs g g, whereby the adjacent screen-plates are interlocked and IOO funnel-shaped. Radially-disposed spaces h 71; are left between said plates forming the screen.

Hitherto the screening-surface has been limited by the shape and diameter ofthe mill, and, from the rapidity with which the machine acts upon material in process of reduction, much difficulty has been experienced in getting rid of the fine-ground material. To overcome this trouble and at the same time increase the screening-surface without increasing the size or diameter of the mill, we have constructed a series of similar] y-shapcd polygonal screen-plates, F F, preferably approximately A-shaped, or in the form ot' truncated prisms in vertical section. These plates are arranged vertically and parallel withl each other, while they project into the interior of the mill beyond the rest of the screening-surface, and rest on the screenholder formed by the curved rings b b. Vhen these screenplates F F are placed in position, they form a roof-shaped screeningsurface which projects into and occupies a portion 'of the interior of the mill, in contradistinction to the other screening portion, which coincides with the interior diameter of the mill. `The interstices j j, formed between two adjacent plates, being vertically situated, are best disposed to facilitate the discharge of the particles passing therethrough. Each of these polygonal screenplates has its sides inclined, so as to converge,

-as shown in Figs. 2 and 3, giving them approximately the shape of the letter A, truncated and with no cross-line. By reference to Figs. Sand 4 the general arrangement and construction' of these polygonal screenplates F will be readily understood.

vIn Fig. 3, which represents a perspective view,'we have shown a plate which, to prevent clogging, is composed of a thin triangular shaped piece, 76 about which, on that portion projecting into the mill, is formed a thickened rim, Z, which inclines on both sides toward the piece 7a. The perimeter of the plate F voperates as the active surface of the screen; hence, as the thickness ofthe individual plates is least in the middle, the spaces j j, formed between the adjacentplates, are best adapted to prevent cloggingthatis,they are V-shaped in crosssection, with the narrow part thereof next the material to be screened, and thus the ground material readily clears itself.

To .interlock and unite the individual plates F F as an entirety, three female lugs, up s, are

cast upon one side of each plate, while upon the opposite side, and correspondingly located, are three male lugs, np s', whereby, when the plates are in position, their adjacent faces are held apart and thus form the interstices or openings j j. The lugs of one plate engage Vthe corresponding lugs uponvthe next plate, and the plates, as a whole, are rigidly secured This may be done by passing bolts together.

It is evident that the polygonal plates may be made of variousheights. Thus the distance which they project beyond the normal screening-surface may be changed to suit circumstances or the material to be ground, and in this manner the screening-surface will beincreased or diminished, respectively, as the l height of the plates F F within the mill is inv creased or diminished. Moreover, the sides of the individual plates F may be changed in their obliquity, or, as shown in Fig. 7,` they may be vertical. This latter form of plate would be better adapted in the event of `employing but one revolving head.

vHaving thus described our invention, what -we claim as new, and desire to secure byLetters Patent, is j 1. The combination, with a curved screen composed of similar plates, a' a', with funnelshaped screening-orifices therebetween, and the truncated prismatic-shaped plates `F. F, projecting beyond the other screenvsurfa'ceof the mill-casing, wherein said screen is secured, and the two rotating grinding-heads, substantially as set forth.

IOO

2. The proj ectng polygonal screen -plates F,

consisting ofthe lateral opposi'tely-disposed lugs n 19 s, n pl` s', the .central reduced plane 'portion kand the thickriml, lpartially surrounding the latterand inclined onboth, sides to its juncture with ,'said. reduced yportion 7c, substantially as herein stated.`

3. A raised roof-shaped screen constructed with the exterior or active screening-surface polygonal to present the largest surface possible, and thereby to increasethe screeningcapacity, substantially as described. e

4. A raised screen composed of a series of screen-plates, theindividual platesbeing arranged to form clearance-spaces therebetween, which are funnel-shaped in cross-section and vertically disposed, substantially as and for the purpose set forth. v

In testimony whereof we aiix our signatures in presence of two witnesses.

THOMAS L. STURTEVANT. MILTON G. DAVIS. l

Witnesses:

H. E. LODGE, F. CURTIS.

IIO

IIS 

